WASHINGTON — Republicans often talk about how they need to do a better job of making inroads into Silicon Valley, the nation’s tech innovation hub, and there have been plenty of reports in recent years about the progress they've already made.

But new data from Crowdpac, a for-profit company that analyzes political giving, demonstrates just how much more often those in Silicon Valley give to Democrats rather than Republicans.

Using that database, Crowdpac derived a list of all the donations from employees of major Silicon Valley tech companies, venture capital firms and the two major research universities in the area, Stanford and the University of California, Berkeley.

The results showed an overwhelming preference in the valley for liberal politicians. And while Republican politicians are making inroads with some key big money donors in the tech capital, the Crowdpac data paints a clear picture of what a challenging environment it is for conservatives. It also helps explain why Republicans find it hard to recruit talent from Silicon Valley to work on their campaigns: Most tech company employees skew left.

Partly this is due to California's politics, where most elected officials statewide and in Congress are Democrats, and to the especially liberal environment in the Bay Area. But as the valley becomes an increasingly lucrative fundraising destination, the GOP will need to do a better job of competing.

Of the tech firms, Twitter has the most liberal employee universe, with 100 percent of its employees’ 23 political donations going to liberal candidates.

Apple Inc. and Google are tied, with 90 percent of their employees' giving going to liberal politicians. Yahoo, LinkedIn, Amazon.com and Facebook all had employees who gave more than 85 percent of their donations to liberals.

Salesforce.com, eBay and PayPal had giving to liberals in the low 80s, while a group of older tech companies — Microsoft, Oracle, HP, Cisco and Intel — showed a slightly more conservative bent in employees’ giving. But at these companies, more than 70 percent of giving still went to liberal candidates.

Of the two universities, Stanford had a higher absolute number of donors to liberal candidates, but Berkeley had a far higher percentage giving to liberals, with 97 percent of its employees who made donations giving to left-of-center candidates. About 91 percent of Stanford's employees whose donations met the reporting threshold gave to left-leaning politicians.

Crowdpac also measured giving from Silicon Valley venture capital firms, where the giving turned out to be more politically balanced. About 57 percent of the giving from these companies was to liberal candidates.

Crowdpac based its ratings of donors on the political ideology of their total giving history, ranking donors on a scale of 1 to 10 for least liberal or conservative to most liberal or conservative. A donor had to have donated money at least twice in order to be given a ranking, said Crowdpac co-founder Steve Hilton, a former aide to British Prime Minister David Cameron.

Based on their rankings of the intensity of donors’ liberalism, Crowdpac’s order of most liberal to least liberal valley companies or institutions went in this order: UC Berkeley, Twitter, Apple, Google, Stanford, Amazon, LinkedIn, Salesforce, Yahoo, eBay, Facebook, Microsoft, PayPal, Cisco, HP, Oracle, Intel and venture capital firms.